Initializes a new `Guard::Plugin` with the given `options` hash. This
methods handles plugins that inherit from the deprecated `Guard::Guard`
class as well as plugins that inherit from `Guard::Plugin`.

the initialized plugin. This return type is deprecated and the plugin's
maintainer should update it to be compatible with Guard 2.0. For more
information on how to upgrade for Guard 2.0, please head over to: github.com/guard/guard/wiki/Upgrading-to-Guard-2.0